This invention relates to a new and improved phase control system for power sources, and more specifically to a control system using bipolar transistors, FETs, IGBTs and gate turn off SCRs to control the on-off power source, with reduced RFI and the virtual elimination of di/dt at turn on. Analogue and digital logic may also be used in the phase control system of this invention.
The use of SCRs for phase control has been well known for many years, and typical publications in this area include: U.S. Pat. Nos. 3,195,038; 3,391,332; 3,412,314; 3,577,177; 3,904,952; 4,174,496; 4,227,029; 4,258,276; 4,380,730; 4,390,795; and, 4,636,935. However, SCRs can not be turned off inside the sine wave but can only be turned on or off at zero cross-over, and hence there is a considerable power loss because the current lags significantly behind the voltage.
Moreover, SCRs produce various problems, such as excessive radio frequency interference due to harmonics caused by the fast turn on, and with the increasing use of computers and many other electronic devices, this RFI is becoming an increasing problem. Also, since the SCR turn on occurs after the cross over point, the current lags significantly behind the voltage, and this reduces the power factor.
A power control system is desired having an improved power factor, by minimizing losses due to di/dt, and also to provide a power control system with a significantly reduced radio frequency interference. It is also desired to provide a power control system which can be modified for both analogue and digital operations, as well as computer control, serial and parallel input, and bridge operations.